Mailvelope

Mailvelope allows to encrypt and decrypt emails in your favorite webmail provider. It integrates directly into the webmail user interface and is easy to use in your regular workflow.
It comes preconfigured for the webmail providers:
• Gmail™
• GMX™
• Outlook.com™
• Posteo™
• WEB.DE™
• Yahoo!™
And can be adjusted to work with other webmail providers. For details, visit https://www.mailvelope.com/help
Mailvelope is completely open source and based on OpenPGP.js (http://openpgpjs.org), an OpenPGP library for JavaScript. The OpenPGP standard (based on PGP as originally developed by Phil Zimmermann) uses a combination of strong public-key and symmetric encryption to secure electronic communication.
Stay informed with Twitter: https://twitter.com/mailvelope
Get the source code on GitHub: https://github.com/mailvelope/mailvelope
Find the latest changelog at: https://github.com/mailvelope/mailvelope/blob/master/Changelog.md